WO 95/00649 (SmithKline Beecham plc) describes the phospholipase A2 enzyme Lipoprotein Associated Phospholipase A2 (Lp-PLA2), the sequence, isolation and purification thereof, isolated nucleic acids encoding the enzyme, and recombinant host cells transformed with DNA encoding the enzyme. Suggested therapeutic uses for inhibitors of the enzyme included atherosclerosis, diabetes, rheumatoid arthritis, stroke, myocardial infarction, reperfusion injury and acute and chronic inflammation. A subsequent publication from the same group further describes this enzyme (Tew D et al, Arterioscler Thromb Vas Biol 1996:16;591-9) wherein it is referred to as LDL-PLA2. A later patent application (WO 95/09921, Icos Corporation) and a related publication in Nature (Tjoelker et al, vol 374, 6 Apr. 1995, 549) describe the enzyme PAF-AH which has essentially the same sequence as Lp-PLA2 and suggest that it may have potential as a therapeutic protein for regulating pathological inflammatory events.
It has been shown that Lp-PLA2 is responsible for the conversion of phosphatidylcholine to lysophosphatidylcholine, during the conversion of low density lipoprotein (LDL) to its oxidised form. The enzyme is known to hydrolyse the sn-2 ester of the oxidised phosphatidylcholine to give lysophosphatidylcholine and an oxidatively modified fatty acid. Both products of Lp-PLA2 action are biologically active with lysophosphatidylcholine, in particular having several pro-atherogenic activities ascribed to it including monocyte chemotaxis and induction of endothelial dysfunction, both of which facilitate monocyte-derived macrophage accumulation within the artery wall. Inhibition of the Lp-PLA2 enzyme would therefore be expected to stop the build up of these macrophage enriched lesions (by inhibition of the formation of lysophosphatidylcholine and oxidised free fatty acids) and so be useful in the treatment of atherosclerosis.
A recently published study (WOSCOPS—Packard et al, N. Engl. J. Med. 343 (2000) 1148-1155) has shown that the level of the enzyme Lp-PLA2 is an independent risk factor in coronary artery disease.
The increased lysophosphatidylcholine content of oxidatively modified LDL is also thought to be responsible for the endothelial dysfunction observed in patients with atherosclerosis. Inhibitors of Lp-PLA2 could therefore prove beneficial in the treatment of this phenomenon. An Lp-PLA2 inhibitor could also find utility in other disease states that exhibit endothelial dysfunction including diabetes, hypertension, angina pectoris and after ischaemia and reperfusion.
Furthermore, Lp-PLA2 inhibitors may also have a general application in any disorder that involves lipid oxidation in conjunction with Lp-PLA2 activity to produce the two injurious products, lysophosphatidylcholine and oxidatively modified fatty acids. Such conditions include the aforementioned conditions atherosclerosis, diabetes, rheumatoid arthritis, stroke, myocardial infarction, ischaemia, reperfusion injury and acute and chronic inflammation.
In addition, Lp-PLA2 inhibitors may also have a general application in any disorder that involves activated monocytes, macrophages or lymphocytes, as all of these cell types express Lp-PLA2. Examples of such disorders include psoriasis.
Furthermore, Lp-PLA2 inhibitors may also have a general application in any disorder that involves lipid oxidation in conjunction with Lp-PLA2 activity to produce the two injurious products, lysophosphatidylcholine and oxidatively modified fatty acids. Such conditions include the aforementioned conditions atherosclerosis, diabetes, rheumatoid arthritis, stroke, myocardial infarction, ischaemia, reperfusion injury and acute and chronic inflammation.
Patent applications WO 01/60805, WO 02/30911, WO 02/30904, WO 03/016287, WO 03/042218, WO 03/042206, WO 03/041712, WO 03/086400, and WO 03/87088 disclose inhibitors of the enzyme Lp-PLA2.